This disclosure relates to providing wireless service to a mobile station in a wireless network and more particularly, but not exclusively, to estimating a geographic location for a mobile station within a coverage area of a wireless network.
Geographic location information for mobile stations has tremendous value to mobile applications, network optimization (e.g., self optimized network (SON)), capacity management, and drive test substitutions, etc. Although many modern mobile stations can obtain their own locations from integrated GPS modules, it is still a challenge for the network to track the locations of a large number of subscribers for an extended period of time. A frequent location update from mobile stations would increase network overhead and may overwhelm the network and create bottlenecks. A passive location estimation technique that leverages measurements from normal network operation is desirable because it avoids such increases in network overhead.
For example, in third generation (3G) code division multiple access (CDMA) networks, such as 3G1X, EVDO, UMTS, etc., one can triangulate the geographic location of a mobile station from the reported round trip delays between the mobile station and three or more base stations (see FIG. 1). The corresponding round trip delays are sent back by the mobile stations for call processing, thus no additional signaling overhead is incurred by the network to collect measurements for triangulation.
However, this triangulation approach does not work in all networks, such as the fourth generation (4G) long term evolution (LTE) networks. Unlike 3G CDMA networks, each measurement report in LTE networks only contains the round trip delay from one cell (i.e., the serving cell of the mobile). Thus, the triangulation technique cannot be used at all in conjunction with 4G LTE networks.
Additionally, geographic location information for mobile stations has tremendous value in compilation and formulation of RF coverage maps for wireless networks. RF coverage maps are useful for management of the network infrastructure and the wireless services provided to users and subscribers. For example, RF coverage maps may be useful to network operators and service providers for troubleshooting and planning for maintenance and upgrades.
However, most of the RF coverage maps are obtained through drive tests. Accurate RF coverage map take hours of drive tests and are very costly. Moreover, as network evolve and environment changes, such as adding new cells or new building construction, the drive tests have to be redone to keep the coverage information up to date. Thus, maintenance of RF coverage maps using drive testing adds even more to the cost.
For these and other reasons, there is a need to provide a technique for estimating a geographic location of a mobile station for at least 4G LTE networks. Additionally, it is desirable that the technique be compatible with other types of wireless networks, especially 3G CDMA networks. It is also desirable that the technique be more reliable than the triangulation technique. Additionally, it is desirable that the technique for estimating a geographic location of a mobile station support construction or maintenance of RF coverage maps in a more cost effective manner than the drive testing technique.